bradley



Feb. 14, 1956 w E, BRADLEY 2,735,032

CATHODE RAY TUBE GUN STRUCTURE Filed OGL. 9, 1952 2 Sheets-Sheet l F/Qn 3.

Feb. 14, 1956 w, E BRADLEY 2,735,032

CATHODE RAY TUBE GUN STRUCTURE Filed OGL. 9, 1952 2 Sheets-Sheet? FVQ". 4.

IN VEN TOR.

U//LL /H/D E. ERHDL BY MUJSG* United States Patent O CATHODE RAY TUBE' GUN STRUCTURE William E. Bradley, New Hope, Pa., assigner to Philco Corporation, Philadelphimla., a corporation of Penn- Sylvania Application Qctober 9, 1952, Serial No. 313,9il7 16 Claims. (Cl. 313-82) The present invention relates to. electron discharge devices and more particularly to improved electron beam generating assemblies for cathode-ray tubes.

The invention is particularly applicable to cathode-ray tubes for producing television images,` in which use the small spot size and large current values of the electron beam produced by the assembly of the inventionbrings` about important improvements inthe reproduced detail and thebrightness of the televised image. While thel invention will be'speciii'cally described in this connection, it should be well understood that the invention is also applicable to other formsof cathode-ray tubes requiring an electron beam having a small spot sizeand/or alargey current capacity.

One of the factors determining the amount of 1mage detail reproducible by the iiuorescent screen ofa cathoderay television tube is the cross-sectional area ofthe spot of the beam generating systemnforexample', by the use of a masking electrode having a small' aperture'and arranged along the path of theV electron stream. However, it is found that this expedient correspondingly reduces the beamV current so this expedient correspondingly reduces the beam current so that the brightness of the image producedk at the screen of the cathode-ray tube is adversely affected to the extent that it is not visually acceptable. While the. beam current may in turnbe increased'by. operating the cathode at' large emission current densities, this remedy isimpracticable because the lifeof the.cathode is shortened prohibitively.

It is an object ofthe invention to provide animproved cathode-ray tube assembly-adapted to produce an electron' beam having a small spot size.

A further object of the invention is to provide anim-V proved cathode-ray tube system adapted to produce a.

beam having a small spot size and a large current capacity without subjecting the source of. the beam to` large ernisf sioncurrent denisities.

Another object of the.inventionis to/provide. anim= proved cathode-ray tube beam generating. system whichis simple to vmanufffrctureand.ofilow cost, andwhich may readily be made within close precisionttolerances.-

Further objects of the inventionwill. appear as the' specification progresses.

In accordance with the invention the foregoing objects are achieved by constructing. the .cathode emissionsurface" of, the beam generatingsystem with aconguration lwhich,

insures that, at anypoint of the: effective .cathode surface, theelectrons are emitted ina direction socorrelated `to theemission vdirectionover the-remainder of the cathode surface, and to .the accelerating-electric field atome-cathode:

surface, that all of the emitted electrons are caused to the image signalapplied' 2f focusv at. substantially thez same point along the axis of the electron, optical systemr formed by the cathode and by the intensity control electrode of the system.

More specifically in: accordance with the invention, a'- beam.' generating and intensity controll system is providedv inl which the peripheral: portions of tlie'etective` emission area of the cathode exhibit a convex contour relative to` they contour: off the central; portions of. the: emission' area so that electrons emitted at the peripheral and central portions; are made: tol converge substantiallyv at the.l same pointalongthe axisof'the system.

Asfafurther feature: of the:l invention, the1 cathode andbeam intensity controlelectrode are constructed' with a spacing and a configuration which establish, over a'majo'r portion of the'eifective emission'su'rface of the cathodeg. a' regionf of intense. voltagev gradienn, and'- equipotentialf lines which arev substantiallyfparallel to` the. surface: of'thev cathode, and' whichinsureslthat. the emission patlisof the electrons conformto a patternas.establishedtby the aforelmentioned shaping of the emissionfsurface.

The inventions will bedescribed: in greater detail witli reference to the appended' drawingsy forming partf of the specification and in which:

Figure'l isa planview, partially inL cross-section, showfing a cathode-ray tube embodying thev novel beam-'gen'- erating assembly of the invention;

Figure 2y is f across-sectional view of: one form.l of a beam generating. assemblyi in=` accordance withy thevv in vention;

Figure 3 is; aplan'view on the assembly off'Fig'ure-Z;

Figurelfis a= cross-sectional view,'.on an enlarged scale, showing. detailsof the beam generatingf assemblyof'th'e' inventionf in accordance withone embodiment thereof;

Figure 5 f is` al cross-sectional view; on ani enlarged-scale, showing details ofanother embodiment of. the'invention; and

Figure.- 6 isa cross-sectionall view, onfanfenlarged scale; showing details of a-further embodimentof theinventionr Referring to: Figure l; the'.v catho'cle'ray. tube' shown therein comprises an evacuated envelopeslllfoffwell known) form` consisting. for example of: glass; Within thef enve lope ltlfthereiarefarranged abeam generating; and controlling system 1-2'. in` accordance. withl the inven'tion-y and' later. to bemorev.fullydescribed, affocusing e1ectro'de114, and a beam accelerating' electrode 15.' whichi may consist? of: a conductive coating=on:the?inner.1 Iwallfof` the envelope in conformity' withz well.- establishedi practice;`

` The end face 18: of the r envelope l 101 mayfbe-y providedy with a beaminterceptingfstructure; the actualco'nsti'uction of which is.E determined by the.' particularfunctionl whichthe cathode-rayxtubefistto. serve. Inone insta-nce, for example; the cathode-ray tubesmay:bensedfor'producing a color television. image in asystem'of the-type disclosed in-the copendingapplicationoffMelvin E; Partin, Serial=No.l 242,264, fledeAugust I7-,- 195i, in'whichA case the beamY intercepting: structure arranged lati ther-faceplate mayy comprise' consecutively.r arranged groups'of 'phosphor' stripes, the stripes of each of vthegroupsfbeing adaptedI to produce light'of three: diiierentfprimary/colors upon electron impingement. In such: anim-rangement; tlieb'eam intercepting structure:A may further comprise'.in'dex'signal generating portions having a geometric configurationin-` dicative of the geometricfconfgnrationof the-'phosphor stripes and adapted tov producean appropriate indexingY signal y upon electron:impingement.` A` beam'A intercepting4 screen .structure off the foregoing dtypexh'as been described: infdetail in the above-mentioned Partini application and a further` description thereof. in.V the present4 application is believed tobe unnecessary;

Asy disclosed.` in thel saidy Partin L application', the beam intercepting. structure-i` is energized. byf an i electron' beam= generating and control system adapted to produce two separate electron beams individually controllable in intensity. One of the beams serves to energize the image producing phosphor stripes, whereas the other beam serves to energize the indexing portions of the screen to produce` an output signal indicative of the position of the beams.

The assembly of the invention is particularly suitable for a dual beam generating and control system for the above indicated purpose, and will be described with specific reference to such a system. However, it should be well understood that the invention is equally applicable to single beam systems and brings about important improvements in the spot size and beam current characteristics of such systems.

A dual beam generating and control system is shown in Figures 2 and 3. The assembly shown, which may be of the general form described and claimed in the cepending application of W. L. Fite et al., Serial No. 367,868 tiled September 4, 1952, comprises a cylindrical member 20 having a tubular body portion 22 extending into an annular end portion 24. The portion 24 may be formed as a separate element and thereafter suitably securedby welding, brazing or the liketo the body portion 22, but is preferably formed as an integral portion of the body portion 22, for example by extrusion. Portions 22 and 24 may consist of nickel, stainless steel, or of other suitable material commonly used in the manufacture of gun assemblies for cathode-ray tubes. At the junction of the body and end portions 22 and 24, the tubular portion 22 is provided with peripheral slots 26 and 28.

Within the sleeve 20 are two intensity control electrodes 34 and 36, each in the form of a spade element extending through one of the peripheral slots 26 and 2S towards the central axis of the sleeve 20. At their inner portions adjacent to the axis of sleeve 20, electrodes 34 and 36 are each provided with an aperture, shown as 38 and 40 respectively, through which pass the respective beams to be individually controlled. The apertures 38 and 40, later to be more fully described, may be of equal dimensions in the event that identical beams are to be formed, or may be of different dimensions where non-similar beams are desired.

Electrodes 34 and 36 are rigidly supported, in an electrically insulated manner, within the sleeve 20 by means of electrically insulating washers 42 and` 44 and by means of a flanged metal ring 46 which may be welded to the inner surface of the sleeve 20. As will be noted, washer 42 is interposed between the electrodes 34-36 and the annular end portion 24, whereas washer 44 is arranged between the said electrodes and the ring 46. By adjusting the compression exerted by the ring 46 against the washer 44, the control electrodes 34 and 36 may be securely positioned within the sleeve 2i). The adjustment by the ring 46 is preferably effected after precisely aligning the electrodes so that the apertures 38 and 40 thereof are arranged on a common diameter and the abutting surfaces of the electrodes form a uniform gap 48 having a width of the order of .062" which has been found to be sufficiently small to establish an electrostatic :field suicient to prevent electrons from passing through the gap under normal operating conditions of the cathode-ray tube.

In practice, the insulating washers 42 and 44 consist of mica; however, it will be apparent that other suitable stable insulating materials such as ceramic materials may be used.

Also positioned within the sleeve 20 is a cathode assembly 50 which may consist of a nickel or stainless steel sleeve 52 open at the bottom end thereof and closed at the top end by a nickel cap 54 to provide a suitable base for an electron emissive coating S6. Coating 56 may be of conventional composition and may consist, for example, of a mixture of barium and strontium oxides.

The cathode assembly 50 is secured within the sleeve 2l) by means of an apertured ceramic disc 58 t0 WhCh 4 the assembly 30 is axed by headings 60 and 62 formed on the periphery of the sleeve 52. For locating the disc 58 within the sleeve 20 there are provided an annular spacer 64 consisting of an insulating material-for example, a ceramic, such as steatite, lavite or the like-one end of which abuts the exposed surface of the mica washer 44 and the other end of which abuts the top surface of the disc S8, and a metal flanged ring 66 which abuts the lower surface of the disc 58 and is welded or otherwise secured to the inner surface of the sleeve 20.

In order to position the electrodes 34 and 36 in a com-` mon plane and at a fixed predetermined distance from the surface of the electron emitting coating 56, insulating spacers 42 and 44 are formed with substantially flat parallel surfaces and the spacing determining elements are formed to precisely controlled dimensions. This may be most simply elfected by the use of mica for the spacers 42 and 44, as above pointed out, since this material splits with substantially parallel surfaces and can be accurately controlled as to its thickness, and by grinding the active surfaces of the spacer 64 and the disc 50.

Desirably the beams emanating from the apertures 38 and 40 are made to converge so that the two beams pass through the same part of the field serving to deflect them throughout the image area. In the arrangement shown in Figure 2, this is effected by means of a converging electrode 68 in the form of an annular metal disc interposed between the insulating washer 42 and the end portion 24 of the member 20; The degree of convergence imparted to the beams may be controlled by adjusting the diameter of the aperture of electrode 68, the spacing between the electrode 68 and electrodes 34-36, and the potential applied to the electrode 68, whereby, the smaller the diameter of the aperture of electrode 68 and/or the greater the spacing between electrode 68 and electrodes 34-36 and/or the less positive the potential of electrode 68, the greater will be the convergence produced by electrode 68. In the arrangement shown, electrode 68 is electrically insulated from the member 20 by means of an insulating washer 70, for example of mica, interposed between electrode 68 and the end portion 24. While the electrode may thus be operated at a potential different from that of sleeve 20 or of the remaining components contained within sleeve 20, in practice the electrode 68 is operated at the same potential as sleeve 20, in which case the insulating washer 70 may be omitted.

A suitable electrical heater (not shown) of well known form may be enclosed within the cathode sleeve 52 to maintain the emissive coating 56 thereof at its electronY emitting temperature.

Electrical connection to the cathode sleeve 52 may be provided by a tab 72 welded thereto, whereas individual electrical connections to the electrodes 34 and 36 may be provided by tab extension portions 74 and 76 respectively of these electrodes. An individual connection to the electrode 68 may be provided by a tab extension portion 78 extending through a peripheral aperture 80 of the sleeve 21. ln practice, the sleeve 20 may be operated at cathode potential, and for this purpose it may be provided with a tab connection 82.

The assembly may be supported within the tube envelope by means of supporting ears 84 which are fused to glass rods 86 (see Figure l) which similarly support the focusing anode 14, and by means of wire standards serving as the connecting elements for the electrodes.

The assembly may be centered within the neck of the cathode-ray tube envelope 10 by a ribbed disc 88 which is welded to the anode 14 and the ribs of which bear against the inner wall of the neck of the envelope.

In accordance with the invention, an electron beamV having a small spot size and large current capacity is achieved by constructing the cathode emission surface with a configuration which insures that, at any point of the effective cathode surface, the electrons are emitted in a direction so correlated to the emission direction over the remainder of the cathode surface that all of the` electrons are focused at substantially the same point along the axis of the electron-optical. systemformed by the cathode and by the intensity control electrode of the system.

More particularly, and inaccordance with the embodiment of the invention shown in Figure 4, the peripheral portion of the elfective emission area of the cathode iS made progressively more convex as al function of the distance from the center of the area so that' the electrons which are emitted by the peripheral portions, and which normally focus at a point relatively close to the cathode surface, are made to focus at a p oint which is further along the axis and thus at a point substantially coincident with the focus point of the centrally emittedv electrons. More specifically, andas will be noted'from Figure 4, an electron emissive coating lili) which is arranged on a base IGZ, and which has an effective surface itil as defined by the projected area of the aperture 104 of an intensity control electrode 196,` is shaped so Athat the peripheral portions 19S of the area lill have a convex configuration, whereas the central portion 1l@ of the area lill is substantially planar and parallel to the plane of the confronting surface of the electrode 106.

By forming the peripheral portions liS with a convex surface, electrons emitted by these portions are made to assume an off-axial velocity so that, in the subsequent acceleration thereof normally produced by the accelerating voltage gradient at the cathode surface, these electrons are made to cross the axis of the system at a more remote position from the cathode surface than would otherwise occur if the cathode surface was not made with such a configuration. Since the central portion llt) of the emission area is planar, the electrons emitted thereby are not correspondingly iniiuenced to any substantial degrec so that these electrons focus at their normal point along the system axis.

The extent of the convex area determined by the dimensions shape of the area fil, and by the distribution of the equipotential lines at the emissive surface. in practice, in the case of a circular emission area as defined by a circular aperture lil-fi, the limits of the convex boundary area as defined by the dimension a in Figure 4 preferably do not exceed about 59% of the radius r of the emission area.

in order to achieve maximum utilization of the benets derived by the compound surface configuration of the emission area as shown in Figure 4, it is desirable t construct the cathode-control electrode system sothat the equipotential lines ot' the accelerating field are substantially parallel to the major portion of the surface of the emission area itil and preferably a large Voltage gradient is produced at the emission surface. To achieve this, the preferred system of the invention is further characterized by a relatively small spacing between the effective plane of the surface of the emission area and the plane of the confronting surface of the control electrode relative to the diameter of the emission rea. For example, the spacing between cathode and control electrode surfaces may be of the order of .0G15 to .005 When the diameter of the aperture lila is of the order of .015". Furthermore, since the intensity of the voltage gradient at the emission surface and the distribution of the equipotential lines are further influenced by the thickness of the con'- trol electrode lod-whereby, in general, the greater the thickness of the control electrode, the smaller the effective size of the aperture and hence the smaller the average voltage gradient and the more curved the contours of the equipotential lines-the size of the aperture 164 is preferably effectively increased by chamfering the edges of electrode ldd which define it, as shown at 112. Since, for a given aperture size and a given thickness of the electrode lido, the chamfer angle determines the effective area of the aperture, the angle should be as large as possible consistent with good heat conductivity at the edges of the aperture. In practice, the charnfer angle 0 may have a value between about 30 and about 60,

is l

and, .for a control electrode .005l 104 havingthe dimensions above have a value at 45.

Instead of constructing the cathode surface so that electrons emitted at the peripheral portions ofthe Vemission area are made to converge at a point more remote than lnormal from the cathode surface, the desired coincidence of the focus point of the centrally and peripherally emitted electrons may be effected. by shortening the focal distance of the centrally emitted electrons. This may be achieved by the arrangement shown in Figure 5 wherein an emissive layer arranged on a base i122', and having an edective emission area 121y as defined by a circular aperture 124 of a control electrode 126, is formed With a concave configuration at the central portion of the emission area as shown at 1123 anda planar peripheral portion as shown at 12g. The degree of curvature of the surface fZ and its extent, are determined by the configuration and operating characteristics ofv thel lens system formed bythe cathode 12til22 and the control electrode 126. Particularly improved results have been obtained when the concave surface l2@ is spherical with a radius of curvature within the range of i20% of the distance between the desired focus point andthe surface of the cathode, and when the surface 12S is restricted so that the dimension c thereof does not exceed about 60% of radius r of the emission area, 121. The construction shown in Figure 5 operates to impart to the electrons emitted by the central portion of the surface 121 an inward radial velocity causing these electrons to focus at a point on the axis` closer to the cathode surface than would normally occur. By this shortening of the focus distance, the focus point of the centrally emitted electrons is made to coincide substantially with the focus point of the peripherally emitted electrons,

Figure 6 illustrates a further modification of the contour of the emission area in accordance with the invention. In Figure 6 an emission layer 130 applied to a base 132, and having an effective emission area 131v as defined by a circular aperture 134 of an intensity control electrode 136, is formed with a convex contour at the peripheral portions as shown at 13S and with a concave contour at the central portion as shown as lidi). As in the case of the constructions shown in Figures 4 and 5, the degree and extent d and e of the curvatures of the surfaces 13S and 14) are determined by the configuration and operating characteristics of the electron lens formed by the cathode Z-M2 and the control electrode ld, and by the desired diminution of the size of the beam spot produced, The limits of curvature and the extent thereof described in connection with Figures 4 and 5 apply equally tothe convex-concave surface shown in Figure 6,

The construction shown in Figure 6, by means of which the focal distance of the peripherally emitted electrons is lengthened and the focal distance of the centrally emitted electrons is shortened to a common coincidence point, brings about beams having extremely small spot sizes. Such small spot beams are particularly desirable for small size camera tubes for television and for Ycolor television image reproducers in which the image screen is in the form of a plurality of adjacently positioned thin phosphor stripes, as above described, or in the form of a plurality of phosphor dots. ln such color image reproducing tubes the beam spot should be smaller than the area of the phosphor deposit to prevent desaturation of the colors of the reproduced image.

While have described my invention by means of specific examples and in a specific embodiment, I do not Wish to be limited thereto for obvious` modications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

l. A cathode-ray tube assembly comprising an evacuated envelope and within said envelope an electron beam generating and intensity control system and a beam intercepting member arranged in spaced relationship to said thick and an aperture noted, the angle 0 may beam generating and control system, said beam generating and control system comprising a cathode electrode and a control electrode arranged in spaced and directly confronting relationship to said cathode and being provided with an aperture, said aperture defining an effective emission area of said cathode and said control electrode being adapted to control the flow of electrons from said effective emission area, said emission area having a surface configuration, a portion of which has a given curvature in a given direction and another portion of which has a curvature in said given direction less than said given curvature, and means for producing at said effective emission area a voltage gradient to accelerate electrons from said emission area through said aperture.

2. A cathode-ray tube assembly as claimed in claim l wherein said peripheral portion of said effective emission area has a convex conguration.

3. A cathode-ray tube assembly as claimed in claim 2 wherein the said effective emission area is substantially circular and wherein the said peripheral portion of convex configuration is limited to a radial distance from the center of said emission area greater than about 50% of the radius of the said emission area.

4. A cathode-ray tube assembly as claimed in claim l wherein said central portion of said effective emission area has a concave configuration.

5. A cathode-ray tube assembly as claimed in claim 4 wherein the said effective emission area is substantially circular and wherein said central portion of concave conliguration is limited to a radial distance from the Center of the said emission area to a value less than j about 60% of the radius of the said emission area.

6. A cathode-ray tube assembly as claimed in claim 4 wherein said central and peripheral portions of the said effective emission area are so configured that the electrons emitted therefrom have substantially coincident focal points and wherein the radius of curvature of the concave central portion has a value within about *:20% of the distance between said focal points and the surface of said emission area.

7. A cathode-ray tube assembly as claimed in claim l wherein said peripheral portion of said effective emission area has a convex configuration and wherein said central portion of said emission area has a planar configuration substantially parallel to the confronting surface of said control electrode.

8. A cathode-ray tube assembly as claimed in claim l wherein said central portion of said effective emission area has a concave configuration and` wherein said peripheral portion of said emission area has a planar configuration substantially parallel to the confronting surface of said control electrode,

9. A cathode-ray tube assembly as claimed in claim l wherein said central portion of said effective emission area has a concave conliguration and wherein said peripheral portion of said emission area has a convex configuration.

10. A cathode-ray tube assembly as claimed in claim 9 wherein the said effective emission area is substantially circular, wherein said concave central portion thereof extends to a radial distance less than about 60% of the radius of said circular area, and wherein said convex peripheral portion thereof extends from a distance more than about 50% of the said radius from the center of said circular area.

1l. A cathode-ray tube assembly as claimed in claim l wherein said aperture has linear dimensions so proportioned relative to the spacing between said cathode and said control electrode that the field produced at said emission surface exhibits equipotential lines substantially parallel to the emission area over substantially the entire surface thereof projected through said aperture.

l2. A cathode-ray tube assembly as claimed in claim l1 wherein said aperture has a chamfered opening the angle of the chamfer of which has a value between 30 and so". t

13. Av cathode-ray tube assembly forl producing two electron beams individually controllable in intensity, comprising a tubular metal member having a cylindrical body portion and a flange portion provided with a central aperture and secured to one end of said body portion, said body portion, at the portion thereof adjacent to said liange portion, being provided wih two diametrically disposed peripheral apertures, first and second beam intensity control electrodes, each having a planar active portion and a planar body portion, said active portions being arranged in juxtaposition and the body portions of said electrodes being arranged substantially in parallel planes and extending through said peripheral apertures, a tirst electrically insulating member having a central aperture and being secured between said ange portion and one side of said body portions of said electrodes, a second electrically insulating member having a central aperture, means to secure said second insulating member in contact with the other side of the body portions of said elec trodes, each of said active portions of said electrodes being provided with an aperture, a cathode assembly having a cylindrical body portion and an end portion, electron emissive material disposed on said last mentioned end portion and forming active surfaces thereon within areas defined by the projections of therespective apertures of said electrodes on said last mentioned end portion, one of said active surfaces having a surface configuration, a portion of which has a given curvature in a given direction with respect to said last mentioned end portion and another portion of which has a curvature in said given direction less than said curvature, and means adapted to produce at said active surfaces a voltage gradient for accelerating electrons from said active areas through said apertures of said active portions of said electrodes.

14. A cathode-ray tube assembly as claimed in claim 13 further comprising an annular electrode member interposed between said first electrically insulating member and said flange portion and adapted to converge electrons accelerated through one of said apertured active portions toward electrons accelerated through the other of said apertured active portions.

15. A cathode-ray tube assembly comprising an evacuated envelope, an electron beam generating and intensity control system Within said envelope, and a beam intercepting member within said envelope arranged in spaced relationship to said beam generating and control system, said beam generating and control system comprising a cathode and an intensity control electrode adjacent thereto, said intensity control electrode having an aperture therein and being spaced from said cathode, said aperture dening an effective emission area of said cathode, said effective emission area having a central portion and a peripheral portion, said peripheral portion having a surface contour which is convex relative to the contour of said central portion, said contours being respectively constructed so that substantially all the electrons emitted therefrom are focussed at a common focal point, and means for producing at said effective emission area a voltage gradient to accelerate said emitted electrons through said aperture. t

16. A cathode-ray tube assembly comprising an evacuated envelope, an electron beam generating and intensity control system within said envelope, and a beam intercepting member within said envelope arranged in spaced relationship to said beam generating and control system, said beam generating and control system comprising a cathode and an intensity control electrode adjacent thereto, said intensity control electrode having an aperture therein and being spaced from said cathode, said aperture defining an effective emission area of said cathode, said emission area having a surface configuration the peripheral portion of which has a given curvature in a given direction and the central portion of which has a. curvature in said given direction less than said given curvature.

References Cited in the file of this patent UNITED STATES PATENTS 10 Painter Aug. 22, 1939 Brunche et al. Nov. 7, 1939 Spanner July 15, 1941 Parker et al Dec. 30, 1941 Winans Dec. 30, 1941 Anderson Jan. 19, 1943 Coleman Mar. 31, 1953 

